app: set default PRACH index for FDD and TDD

Author: herlesupreeth

apps/gnb/gnb_appconfig_translators.cpp

@@ -1445,18 +1445,13 @@ static void derive_cell_auto_params(base_cell_appconfig& cell_cfg)
     cell_cfg.tdd_ul_dl_cfg->pattern1.nof_ul_symbols     = 0;
   }
 
-  // If PRACH configuration Index not set, derive a valid one.
+  // If PRACH configuration Index not set, a default one is assigned.
   if (not cell_cfg.prach_cfg.prach_config_index.has_value()) {
     if (band_helper::get_duplex_mode(cell_cfg.band.value()) == duplex_mode::FDD) {
-      cell_cfg.prach_cfg.prach_config_index = 1;
+      cell_cfg.prach_cfg.prach_config_index = 16;
     } else {
-      // TDD case. Ensure the PRACH falls in UL slots.
-      optional<uint8_t> index_found = prach_helper::find_valid_prach_config_index(
-          cell_cfg.common_scs, generate_tdd_pattern(cell_cfg.common_scs, cell_cfg.tdd_ul_dl_cfg.value()));
-      if (not index_found.has_value()) {
-        report_error("Failed to auto-derive PRACH configuration index");
-      }
-      cell_cfg.prach_cfg.prach_config_index = *index_found;
+      // Valid for TDD period of 5 ms. And, PRACH index 159 is well tested.
+      cell_cfg.prach_cfg.prach_config_index = 159;
     }
   }
 }

apps/gnb/gnb_appconfig_validators.cpp

@@ -206,7 +206,7 @@ static bool validate_pucch_cell_app_config(const base_cell_appconfig& config)
 /// Validates the given PRACH cell application configuration. Returns true on success, otherwise false.
 static bool validate_prach_cell_app_config(const prach_appconfig& config, nr_band band)
 {
-  srsran_assert(config.prach_config_index.has_value(), "The PRACH configuration index must be set or auto-derived.");
+  srsran_assert(config.prach_config_index.has_value(), "The PRACH configuration index must be set.");
 
   auto code =
       prach_helper::prach_config_index_is_valid(config.prach_config_index.value(), band_helper::get_duplex_mode(band));

include/srsran/ran/prach/prach_helper.h

@@ -38,7 +38,9 @@ error_type<interval<uint8_t>>
 prach_fits_in_tdd_pattern(subcarrier_spacing pusch_scs, uint8_t prach_cfg_idx, const tdd_ul_dl_config_common& tdd_cfg);
 
 /// \brief Finds a PRACH configuration index that ensures that PRACH falls in an TDD UL slot.
-optional<uint8_t> find_valid_prach_config_index(subcarrier_spacing pusch_scs, const tdd_ul_dl_config_common& tdd_cfg);
+optional<uint8_t> find_valid_prach_config_index(subcarrier_spacing             pusch_scs,
+                                                uint8_t                        zero_correlation_zone,
+                                                const tdd_ul_dl_config_common& tdd_cfg);
 
 } // namespace prach_helper
-} // namespace srsran
+} // namespace srsran

lib/ran/prach/prach_helper.cpp

@@ -54,7 +54,7 @@ error_type<std::string> srsran::prach_helper::zero_correlation_zone_is_valid(uin
     if ((prach_config.format == prach_format_type::B4) && (zero_correlation_zone != 0) &&
         (zero_correlation_zone != 14)) {
       return fmt::format(
-          "PRACH Zero Correlation Zone index (i.e., {}) with Format B4 is not supported for FDD. Use 0 or 14.\n",
+          "PRACH Zero Correlation Zone index (i.e., {}) with Format B4 is not supported for TDD. Use 0 or 14.\n",
           zero_correlation_zone);
     }
   }
@@ -93,14 +93,16 @@ error_type<interval<uint8_t>> srsran::prach_helper::prach_fits_in_tdd_pattern(su
   return {};
 }
 
-optional<uint8_t> srsran::prach_helper::find_valid_prach_config_index(subcarrier_spacing             pusch_scs,
+optional<uint8_t> srsran::prach_helper::find_valid_prach_config_index(subcarrier_spacing pusch_scs,
+                                                                      uint8_t            zero_correlation_zone,
                                                                       const tdd_ul_dl_config_common& tdd_cfg)
 {
   static constexpr size_t NOF_PRACH_CONFIG_INDEXES = 256;
 
   // Iterate over different PRACH configuration indexes until a valid one is found.
   for (unsigned prach_cfg_idx = 0; prach_cfg_idx != NOF_PRACH_CONFIG_INDEXES; ++prach_cfg_idx) {
     if (prach_config_index_is_valid(prach_cfg_idx, duplex_mode::TDD).has_value() and
+        zero_correlation_zone_is_valid(zero_correlation_zone, prach_cfg_idx, duplex_mode::TDD).has_value() and
         prach_fits_in_tdd_pattern(pusch_scs, prach_cfg_idx, tdd_cfg).has_value()) {
       return prach_cfg_idx;
     }

lib/scheduler/config/serving_cell_config_factory.cpp

@@ -338,10 +338,13 @@ srsran::config_helpers::make_default_ul_config_common(const cell_config_builder_
   cfg.freq_info_ul.freq_band_list.back().band = *params.band;
   cfg.init_ul_bwp.generic_params              = make_default_init_bwp(params);
   cfg.init_ul_bwp.rach_cfg_common.emplace();
-  cfg.init_ul_bwp.rach_cfg_common->rach_cfg_generic.prach_config_index = 1;
+  cfg.init_ul_bwp.rach_cfg_common->rach_cfg_generic.zero_correlation_zone_config = 15;
+  cfg.init_ul_bwp.rach_cfg_common->rach_cfg_generic.prach_config_index           = 16;
   if (band_helper::get_duplex_mode(params.band.value()) == duplex_mode::TDD) {
-    optional<uint8_t> idx_found =
-        prach_helper::find_valid_prach_config_index(params.scs_common, *params.tdd_ul_dl_cfg_common);
+    optional<uint8_t> idx_found = prach_helper::find_valid_prach_config_index(
+        params.scs_common,
+        cfg.init_ul_bwp.rach_cfg_common->rach_cfg_generic.zero_correlation_zone_config,
+        *params.tdd_ul_dl_cfg_common);
     srsran_assert(idx_found.has_value(), "Unable to find a PRACH config index for the given TDD pattern");
     cfg.init_ul_bwp.rach_cfg_common->rach_cfg_generic.prach_config_index = idx_found.value();
   }
@@ -365,8 +368,8 @@ srsran::config_helpers::make_default_ul_config_common(const cell_config_builder_
   cfg.init_ul_bwp.rach_cfg_common->msg3_transform_precoder   = false;
   cfg.init_ul_bwp.rach_cfg_common->rach_cfg_generic.msg1_fdm = 1;
   // Add +3 PRBS to the MSG1 frequency start, which act as a guardband between the PUCCH and PRACH.
-  cfg.init_ul_bwp.rach_cfg_common->rach_cfg_generic.msg1_frequency_start         = 6;
-  cfg.init_ul_bwp.rach_cfg_common->rach_cfg_generic.zero_correlation_zone_config = 15;
+  cfg.init_ul_bwp.rach_cfg_common->rach_cfg_generic.msg1_frequency_start = 6;
+
   cfg.init_ul_bwp.rach_cfg_common->rach_cfg_generic.ra_resp_window = 10U << to_numerology_value(params.scs_common);
   cfg.init_ul_bwp.rach_cfg_common->rach_cfg_generic.preamble_rx_target_pw = -100;
   cfg.init_ul_bwp.pusch_cfg_common.emplace();